Concept drawings (also referred to as concept sketches) are used by artists and designers to convey the shapes of objects. Examples of concept drawings 10A and 10B (collectively, concept drawings 10) are shown in FIGS. 1A and 1B (collectively, FIG. 1). Concept drawing 10A of FIG. 1A is drawing of a hand cream container and concept drawing 10B of FIG. 1B is a drawing of a sports bag. The hand cream container and the sports bag may be referred to herein as the objects underlying concept drawings 10A, 10B, respectively. Concept drawings (whether drawn on paper or represented in a computer) typically comprise a plurality of two-dimensional curves which are used by the artist or designer to convey to observers three-dimensional information about the objects underlying the drawings. Concept drawings 10 typically include a number of types of two-dimensional curves. Boundary curves 11A, 11B (collectively, boundary curves 11) demarcate parts of the object underlying concept drawings 10. Boundary curves 11 may include smooth silhouette curves (or, for brevity, silhouettes) 12A, 12B (collectively, silhouettes 12) and sharp boundary curves (or, for brevity, sharp boundaries) 14A, 14B (collectively, sharp boundaries 14). Silhouettes 12 may demarcate transitions between visible and hidden parts of a smooth surface and may be dependent on the views depicted in concept drawings 10. In mathematical terms, silhouettes 12 may demarcate parts of concept drawings 10 where the surface normal of the objects underlying the concept drawings 10 transitions from facing toward the viewer to facing away from the viewer. Sharp boundaries 14 can demarcate ends of surfaces, junctions between different parts of objects, sharp bends on surfaces, discontinuous transitions and/or the like. In some views and/or for some objects boundary curves 11 can be both silhouettes 12 and sharp boundaries 14 or such silhouettes 12 and sharp boundaries 14 may overlap.
In addition to boundary curves, artists and designers typically use cross-section curves (or, for brevity, cross-sections) 16A, 16B (collectively, cross-sections 16) which aid in the drawing of concept sketches 10 and in the viewer's interpretation of the three-dimensional appearance of objects underlying concept sketches 10. The intersections of cross-sections 16 may be referred to as cross-hairs 18. When drawn in concept sketches (on paper or on computer representations), cross-sections 16 are only two-dimensional. However, cross-sections 16 are used to convey three-dimensional information about the objects underlying the concept drawings by depicting intersections of imagined three-dimensional surfaces with three-dimensional planes. Cross-sections 16 and cross-hairs 18 carry important perceptual information for viewers and are typically drawn at or near locations where they maximize (or at least improve) the clarity of concept sketches 10.
There is a general desire to characterize concept drawings 10. Such characterization may comprise generating three-dimensional information based on two-dimensional concept drawings 10.
The foregoing examples of the related art and limitations are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.